1. Field of the Invention
The present invention relates to information traffic and performance monitoring in a multi-beam satellite network with on-board switching.
2. Description of the Related Art
Traffic monitoring is used for gathering usage information for billing, traffic policing to ensure that user traffic does not cause congestion in the network, and collecting statistics for resource planning.
During traffic monitoring for circuit switched traffic, a user terminal (UT) is assigned a fixed radio resource to a fixed destination terminal. Neither the required radio resource nor the destination of the traffic changes throughout the call. The only traffic statistics are the duration of the call, the identity of the origination and destination terminals, and the size of the radio resource assigned to the call. All of this information can be obtained during connection establishment and connection tear down signaling between the UT and a central location such as a Network Control Center (NCC).
During traffic monitoring for packet based traffic, traffic intensity (measured in bits/s or packets/s) may change during the life-time of the connection requiring the NCC to vary the radio resource assigned to the connection to match the demand. When a network accepts such a connection, there is a mutual agreement between the UT and the network. The UT specifies the traffic characteristics for the connection and the network guarantees to provide the quality of service (QoS) required by the connection. This is called a traffic contract. A traffic contract includes the connection""s traffic characteristics, the required QoS, and the destination terminal. The traffic characteristics are typically specified in terms of maximum bit rate, average bit rate, and maximum burst length, i.e., the length of the time period during which the terminal transmits at the peak rate. The NCC checks the availability of radio resources, traffic statistics, and required QOS of on-going connections, and decides whether a new call can be accepted into the network. Usually, the new connection will conform to its traffic description.
The amount of radio resources assigned to a connection depends on both the traffic characteristics and the required QoS. Two connections with identical traffic characteristics and different QoS requirements will require a different amount of radio resource. For example, delay tolerant traffic can be assigned a transmission capacity that is very close to the mean bit rate requirement of the connection. Instantaneous periods of high activity can be handled by buffering and temporarily increasing the transmission capacity. On the other hand, delay sensitive traffic would be assigned a transmission capacity equivalent to the peak transmission rate of the connection or very close to it. When additional resources are available, a higher transmission capacity can be assigned to the delay tolerant connection than what is actually needed in order to improve performance.
Even if the transmission capacity assigned to a connection can be higher than the connection""s mean traffic rate, it is necessary that the traffic generated by the UT conform to the traffic contract. A UT with an assigned transmission capacity higher than the mean transmission rate specified in the traffic contract can potentially exceed the mean transmission rate and cause congestion in the network. In a satellite network with an on-board packet switch, congestion can occur at a switch output port, thereby degrading the performance of all connections using that output port. Therefore, it is very important that in a satellite system, where the radio resource assigned to a connection is higher than the mean transmission rate specified in the traffic contract, steps are taken to monitor and police the traffic. In addition, In such a network since the transmission capacity assigned to the connection can be larger than what the connection actually uses, billing cannot be based on the assigned capacity alone.
Performance monitoring refers to transmission link performance monitoring. Link degradations can be caused from adverse weather conditions, satellite equipment malfunctioning, and interference. It is important to discover these degradations quickly and take counter measures such as rerouting of traffic or enforcing of transmission power levels.
Conventionally, traffic monitoring can be performed at the UTs or the satellite. Performance monitoring can be performed at the UTs.
When traffic monitoring is performed by the UT, the UT is provided with the capability to collect usage statistics on each connection and send them to the NCC periodically or upon request. The UT must be secured to prevent tampering with the collected statistics.
The capability to perform traffic policing can also be implemented at the UT. The policing unit of the UT is provided with the traffic description of each connection at connection setup. All traffic passes through the policing unit before it is transmitted to the satellite. The policing unit ensures that traffic sent to the satellite conforms to the traffic description by performing traffic shaping or blocking. The policing unit must be secured to prevent tampering.
When traffic monitoring Is performed on the satellite, the on-board processor is provided with the capability to collect usage statistics on each connection and send them to the NCC periodically or upon request.
The up link processors are provided with the capability to police each connection. The policing units of the satellite are provided with each connection""s traffic description upon connection setup. All uplink traffic passes through the policing units before entering the on-board switch. The policing units ensure that traffic sent to the satellite from the UTs conforms connection traffic descriptions by performing traffic shaping or blocking.
Each UT monitors the link performance by measuring bit error statistics on down-link transmission. These measurements are sent to the NCC periodically or upon request.
Implementing the monitoring functions at the UTs has three main disadvantages: i) cost and complexity, ii) security, and iii) traffic overhead. First, cost is one of the most important concerns in terminal design especially for consumer terminals. The cost associated with traffic monitoring and performance monitoring can be a significant portion of UT cost. Second, where possible, billing related information should not be collected and stored at the customer equipment due to security concerns. The same concern applies to traffic policing as well. Implementing a totally fraud proof traffic monitoring function can increase the UT cost further. Lastly, there is a communications resource overhead associated with gathering traffic and performance information at each UT and reporting them periodically to the NCC. Centralized monitoring and collective reporting of such data reduces overall communications resource requirements.
The satellite is the ideal place for implementing traffic monitoring functions as this maximizes security and minimizes communications resources associated with reporting of these statistics to the NCC. However, implementing the monitoring functions at the satellite requires capability to collect individual usage statistics and perform individual traffic policing for each connection that the satellite is serving. This increases on-board processing requirements significantly and may not be technically feasible for a large network due to payload mass and power constraints. In addition, centralizing the monitoring functions at the satellite may not be desirable due to reliability considerations. Lastly, transmission link performance monitoring cannot be performed at the satellite and would still need to be implemented on-ground.
To solve the above problems, it is an object of the present invention to provide an information traffic and performance monitoring system using monitoring functions performed by a number of specially equipped ground terminals, xe2x80x9cmonitoring terminalsxe2x80x9d (MT). MTs are low-cost terminals dedicated to performing traffic and performance monitoring and reporting functions. At least one MT is placed at each satellite beam to monitor the traffic of all connections on that down-link beam. The MT also monitors the link performance in that area. Collected statistics are sent to the NCC periodically or upon request.
Accordingly, to achieve the above object, there is provided an information traffic and performance monitoring system for multi-beam satellites with on-board switching containing a satellite for providing communication between a user terminal and a destination user terminal forming a connection. There also is provided a system between MTs and a central location, the system comprising a user terminal for transmitting information to and receiving information from the destination user. terminal and forming a flow of connection with the destination user terminal. There also is at least one MT located in each satellite beam for monitoring the traffic information and the performance of all connections in the satellite beam. Finally, there is a central location for communicating with each of the MTs.